CN110024054B

CN110024054B - Thermally protected metal oxide piezoresistor

Info

Publication number: CN110024054B
Application number: CN201780018399.8A
Authority: CN
Inventors: 宋东健; 陆利兵
Original assignee: Dongguan Littelfuse Electronic Co Ltd
Current assignee: Dongguan Littelfuse Electronic Co Ltd
Priority date: 2017-10-13
Filing date: 2017-10-13
Publication date: 2021-06-29
Anticipated expiration: 2037-10-13
Also published as: CN110024054A; WO2019071841A1; CN109923625A; WO2019071588A1; CN109923625B

Abstract

Thermally Protected Varistor (TPV) devices are provided herein. The TPV device also includes a terminal assembly coupled to the piezoresistor body, the terminal assembly including a housing having sidewalls and a base, the base including an opening formed therethrough. The spring elements (e.g., spring elements) of the terminal assemblies include a first end disposed within the housing and a second end extending outside of the housing. The first terminal of the spring element engages the thermode of the varistor body through the opening of the base and maintains or breaks contact depending on whether the thermal link material (e.g., solder) coupling the thermode to the spring element is below or above the melting point (e.g., during an overvoltage fault condition). The TPV device can also include an inner electrode extending through an opening in the base of the housing for engagement with the spring element.

Description

Thermally protected metal oxide piezoresistor

Technical Field

The present disclosure relates generally to protecting electrical and electronic circuits and equipment from electrical surges, and more particularly to a thermally protected piezoresistor (varistor) with thermally actuated disconnection.

Background

Overvoltage protection devices are used to protect electronic circuits and components from damage due to overvoltage fault conditions. These overvoltage protection devices may include a Metal Oxide Varistor (MOV) connected between the circuit to be protected and ground. MOVs have specific current-voltage characteristics that allow them to be used to protect these circuits from catastrophic voltage surges. Typically, these devices utilize spring elements that melt under abnormal conditions to form an open circuit. In particular, when a voltage greater than the nominal or threshold voltage is applied to the device, current flows through the MOV, which generates heat. This causes the link element to melt. Once the link melts, an open circuit is created, which prevents the MOV from firing.

However, these prior circuit protection devices do not provide efficient heat transfer from the MOV to the spring element, thereby delaying the response time and subjecting the MOV to periodic transient voltage and overvoltage conditions, which apply further electrical stress. Due to these stresses, the MOV tends to degrade over time, resulting in higher leakage currents. At the end of its electrical life, the MOV tends to fail catastrophically. End-of-life faults come in a variety of forms. The failure caused by fragmentation due to excessive transient voltages is a type of end-of-life failure. Another type of fault is thermal runaway caused by degradation of the MOV and/or sustained abnormal overvoltage conditions. Thermal disconnection is used to open the device in the event of sustained overvoltage or thermal runaway due in part to the electrical stress described above. It is desirable to have the thermal disconnect mechanism very close to the MOV pad so that the thermal response time is as fast as possible. The purpose of thermally opening the MOV is therefore to provide a relatively benign failure when subjected to conditions leading to thermal runaway.

While thermally protective piezoresistors are currently available, the currently available thermally breaking piezoresistors comprise complex components and are costly to manufacture. Another disadvantage of known thermally protected varistor solutions is that they are single-use components that must be replaced once the thermal disconnection is triggered. Since the thermal disconnect is typically enclosed in a housing, an individual servicing the equipment may not be able to readily determine when the thermal disconnect is triggered and needs to be replaced.

Accordingly, there is a current need for an efficiently constructed piezoresistor that can be easily maintained and serviced for protecting sensitive circuits and equipment from abnormal overvoltage transients. It is based on these and other considerations that current improvements are provided.

Disclosure of Invention

In one aspect according to the present disclosure, a Thermally Protected Varistor (TPV) device may include a varistor body having an electrode disposed along a first side and a hot electrode disposed along a second side opposite the first side, wherein a first lead is electrically connected to the electrode and a second lead is electrically connected to the hot electrode. The TPV device can further include a terminal assembly coupled to the piezoresistor body, the terminal assembly including a housing including a sidewall and a base, wherein an opening is provided in the base; and a spring element having a first end disposed within the housing and a second end extending outside the housing. A first terminal at a first end of the spring element may be connected with the thermode through an opening of the base to maintain the spring element in physical contact with the thermode when a thermal link material coupling the spring element and the thermode is below a melting point. Further, a second terminal at the second end of the spring element may be connected to the third lead.

In another aspect according to the present disclosure, a Thermally Protected Varistor (TPV) device includes a varistor body having an electrode disposed along a first side and a hot electrode disposed along a second side opposite the first side, with a first lead electrically connected to the electrode and a second lead electrically connected to the hot electrode. The TPV device can further include a terminal assembly coupled to the varistor body, the terminal assembly including a housing including a sidewall and a base, wherein an opening is provided in the base for electrical connection with the hot electrode; and a spring element having a first end disposed within the housing and a second end extending outside the housing through a slot in the sidewall. The first end may be connected to the thermode through an opening of the base to maintain the spring element in physical contact with the thermode via the thermal link material when the thermal link material is below a thermal threshold. Further, a second terminal at the second end may be connected to the third lead.

Drawings

The accompanying drawings illustrate exemplary aspects of the embodiments disclosed thus far designed for practical application of the principles thereof, and wherein:

fig. 1 depicts a circuit diagram including a TPV device according to an embodiment of the present disclosure;

2-5 depict a TPV device according to embodiments of the present disclosure;

6-9 depict terminal assemblies of the TPV apparatus of FIGS. 2-5 in accordance with embodiments of the present disclosure;

figure 10 depicts a spring element of the TPV device of figures 2-5 in accordance with an embodiment of the present disclosure;

figure 11 depicts a TPV device according to an embodiment of the present disclosure;

fig. 12 depicts a terminal assembly of the TPV device of fig. 11 in accordance with an exemplary embodiment of the present disclosure;

figures 13-15 depict a TPV device according to embodiments of the present disclosure;

figures 16-17 depict terminal assemblies of the TPV devices of figures 13-15, according to embodiments of the present disclosure;

figure 18 depicts a spring element of the TPV device of figures 13-15 in accordance with an embodiment of the present disclosure;

19-21 depict a TPV device according to embodiments of the present disclosure; and

fig. 22 depicts a spring element of the TPV device of fig. 19-21 in accordance with an embodiment of the present disclosure.

The drawings are not necessarily to scale. The drawings are merely representations, not intended to portray specific parameters of the disclosure. The drawings are intended to depict typical embodiments of the disclosure, and therefore should not be considered as limiting the scope. In the drawings, like numbering represents like elements.

Moreover, for clarity of illustration, some elements in the figures may be omitted or not shown to scale. Moreover, some reference numerals may be omitted in some drawings for clarity.

Detailed Description

Embodiments in accordance with the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings. The system/circuit may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the systems and methods to those skilled in the art.

For convenience and clarity, terms such as "top," "bottom," "upper," "lower," "vertical," "horizontal," "transverse," and "longitudinal" will be used herein to describe the relative placement and orientation of the various components and their constituents. The terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.

As used herein, an element or operation recited in the singular and proceeded with the word "a" or "an" should be understood as not excluding plural elements or operations, unless such exclusion is explicitly recited. Furthermore, references to "one embodiment" of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

Furthermore, in the following description and/or claims, the terms "on.. times," "overlying … …," "disposed on.. times," and "above.. times" may be used in the following description and claims. "on.. times," "overlying … …," "disposed on.. times," and "over.. times" may be used to indicate that two or more elements are in direct physical contact with each other. However, "on.. over," overlies … …, "" is disposed on.. and "is above" may also mean that two or more elements are not in direct contact with each other. For example, "over" may mean that one element is over another element but not in contact with each other and that there may be another element or elements between the two elements. Furthermore, the term "and/or" may mean "and," it may mean "or," it may mean "exclusive or," it may mean "one," it may mean "some, but not all," it may mean "neither" and/or it may mean "both," although the scope of claimed subject matter is not limited in this respect.

As will be described herein, a Thermal Protection Varistor (TPV) device is provided that includes a varistor body having electrodes connected to a plurality of leads. The TPV device also includes a terminal assembly connected to the varistor body, the terminal assembly including a housing having sidewalls and a base, the base including an opening formed therethrough for connection between the hot electrode of the varistor body and the terminal. The spring elements (e.g., metal contacts/terminals exhibiting spring characteristics) of the terminal assemblies include a first end disposed within the housing and a second end extending outside the housing. The terminals of the spring element engage the thermodes of the varistor body and maintain or break contact depending on whether the thermal link material (e.g., solder) coupling the thermodes to the spring element is below or above a thermal threshold, such as a melting point in the event of an overvoltage fault. The TPV device can also include an inner electrode extending through an opening in the base of the housing for engagement with the spring element.

As will be apparent herein, the TPV device of the present disclosure can solve the problems of the prior art, i.e., high cost and low reliability, by forming a highly reliable open circuit using a ceramic fuse coupled with a spring terminal. The TPV device may protect the circuit from damage during an over-temperature event caused by an abnormal over-voltage condition.

Turning now to fig. 1, a thermal protection piezoresistor (TPV) device 10 for use with the circuit 2 in accordance with an embodiment of the present disclosure will be described. The simplified circuit 2 generally comprises a TPV device 10, a power supply 3 and a protected circuit or equipment 4. As will be understood by those skilled in the art, during normal operation, the TPV device 10, which may be positioned in parallel between the first terminal of the power source 3 and the protected circuit 4, is in a closed or conducting position, and the protected circuit 4 is powered by the power source 3. As will be described below, the TPV device 10 is turned on (as shown) in an overvoltage condition. The circuit 2 described herein is not intended to be limiting, but merely provides an illustrative example of a general circuit for the context.

Turning now to fig. 2-4, a TPV device 10 in accordance with an embodiment of the present disclosure will be described in more detail. As shown, the TPV device 10 includes a varistor body 12, which in this embodiment has a circular or disc shape generally defined by an outer periphery 13. The varistor body 12 includes a first electrode 14 disposed along a first side 16 and a hot electrode 18 disposed along a second side 20. The first lead 21 is electrically connected to the first electrode 14, and the second lead 22 is electrically connected to the hot electrode 18. In some embodiments, thermode 18 is a metallized layer of ceramic, silver, copper, aluminum, or copper plus aluminum.

The TPV device 10 can also include a terminal assembly 24 (fig. 4) coupled to the varistor body 12. In some embodiments, the terminal assembly 24 includes a housing 26 having sidewalls 28 and a base 30, wherein the sidewalls 28 extend substantially around the perimeter of the housing 26. The sidewall 28 and base 30 define a central cavity 32 in which a spring element 35 is contained. The spring element 35 includes a first end 36 disposed within the housing 26 and a second end 37 extending outside of the housing 26. The second end 37 is connected to the third lead 23. As will be described in greater detail below, the first terminal at the first end 36 may be connected with the thermode 18 through an opening of the base 30 to maintain the spring element 35 in physical/electrical contact with the thermode 18 when a thermal link element (e.g., solder) coupling the spring element 35 to the thermode 18 is below a melting point. If the thermal link element exceeds the melting point, for example, in the event of an overcurrent condition, the spring element 35 will disengage and move away from the hot electrode 18 exposed through the opening 44, thereby causing the third lead 23 to be disconnected from the power source.

The TPV device 10 also includes a housing cover 39 coupled to the housing 26 and/or the varistor body 12. In some embodiments, the housing cover 39 may generally follow the shape of the housing 26. As shown, the housing cap 39 may take the shape of a mushroom defined by a head 40, a neck 41 and a pair of cutouts 42. As best shown in fig. 2, the pair of notches 42 provide an area for the second wire 22 to approach/contact the hot electrode 18. In some embodiments, the housing cap 39 may include an opening or slot 43 through the neck 41 from which the second end 37 of the spring element 35 may protrude. Although not shown, the TPV device 10 can also include a conformal epoxy or other high insulation material surrounding the piezoresistor body 12, the terminal assembly 24, and the housing cover 39.

Turning now to fig. 5-9, the terminal assembly 24 of the TPV device 10 according to embodiments of the present disclosure will be described in greater detail. As shown, the terminal assembly 24 includes a spring element 35 secured to the hot electrode 18 via an opening 44 formed through the base 30 of the housing 26. More specifically, the first terminal 45 at the first end 36 of the spring element 35 may be connected to the hot electrode 18 using a thermal link material 48 (such as a low temperature solder). The first terminal 45 may include one or more protrusions 50 extending therefrom to allow for an area of thermal link material 48 to accumulate between the first end 36 of the spring element 35 and the hot electrode 18. In some embodiments, the thermal link material 48 is disposed primarily along the exposed surface of the thermode 18. In other embodiments, the thermal link material 48 is disposed primarily along the first end 36 of the spring element 35.

When the thermal link material 48 is below the melting point, physical/electrical contact between the first terminal 45 and the hot electrode 18 is maintained, thereby positioning the first terminal 45 over the opening 44. However, when the hot electrode 18 heats up and exceeds the melting point of the thermal link material 48, the thermal link material 48 melts and begins to flow, creating an insulating gap between the hot electrode 18 and the first terminal 45 of the spring element 35. During an overcurrent event, the first end 36 of the spring element 35 is configured to move from the position shown in fig. 5-6 to the position shown in fig. 7-8 due to the biasing spring force of the spring element 35. In some embodiments, when the spring element 35 is disconnected from the hot electrode 18, the first end 36 of the spring element 35 is received within the guide area 49, the guide area 49 being recessed into the base 30 of the housing 26. The guide region 49 may provide clearance for the protrusion 50 when the spring element 35 is swung within the cavity 32 of the housing 26.

As further shown, the terminal assembly 24 may include one or more terminal clips 51 secured to the housing 26 and the varistor body 12. In some embodiments, the terminal clips 51 are each a substantially U-shaped fastener that is secured around an attachment member 52 extending from the side wall 28 of the housing 26. For example, as best shown in fig. 6, one leg of the terminal clip 51 may extend substantially parallel to the bottom surface 53 of the base 30 of the housing 26. The other leg may include a ridge or lip 55, which is a mechanical piece designed to mate or engage with a corresponding surface feature (e.g., notch) of the attachment member 52 to secure the terminal clip 51 in place. The outer surface 54 of each terminal clip 51 may be secured (e.g., by high temperature solder) to the varistor body 12, e.g., directly to the thermode 18. During assembly, the terminal clip 51 may be first secured to the varistor body 12 so that the housing 26 may then be snapped into place during assembly. However, it should be appreciated that the above-described attachment configuration is non-limiting, as other arrangements for releasably securing the housing 26 to the varistor body 12 are possible within the scope of the present disclosure. Further, the terminal clip 51 is not limited to any particular material, but may include pre-tinned SUS or pre-tinned steel in an exemplary embodiment.

The housing 26 of the terminal assembly 24 also includes first and

second support walls

57, 58, the first and

second support walls

57, 58 defining a channel 59 for receiving and securing the spring element 35 therein. The channel 59 defines an opening or slot 60 extending through the sidewall 28 to allow the second end 37 of the spring element 35 to extend outside of the housing 26 for connection with the third lead 23. The housing 26 also includes a support post 62 adjacent to and extending from the first support wall 57. As shown, the spring element 35 is at least partially bent around the support post 62 to provide tension to the spring element 35. In some embodiments, the housing 26 may be a high temperature plastic or resin. Such as polyphenylene sulfide (PPS), Liquid Crystal Polymer (LCP), and the like.

As best shown in fig. 9, the spring element 35 includes a central portion 65 extending between the first end 36 and the second end 37, wherein the central portion 65 may include one or more bending features to mitigate stress concentrations due to fatigue and temperature fluctuations over time. For example, central portion 65 may include a first bend 66 proximate first end 36, and a second bend 67 between first bend 66 and second end 37. The second bend 67 is located proximate an angular joint 68, the angular joint 68 having a first portion 69 configured to extend through the channel 59 of the housing 26 and a second portion 70 configured to extend through the slot 60. As further shown, the first terminal 45 may extend perpendicularly from the central portion 65 to enable contact with the hot electrode 18. Although not limited to any particular material, the spring element 35 may be beryllium copper, tin bronze, or other flexible metallic material.

In some embodiments, corner joint 68 has a first height dimension H1, which is H1 greater/longer than a second height dimension H2 adjacent central portion 65 and first end 36. The height difference between H1 and H2 is designed to allow the spring element 35 to swing freely from the base 30 of the housing 26 with minimal friction during an over-current event. As further shown, the second end 37 of the spring element 35 also includes a second terminal 74 for electrically/physically coupling the spring element 35 with the third lead 23. In some embodiments, the second terminal 74 may include sidewalls 80, 81 that define a channel 73 for receiving the third lead 23 therein. The second terminal 74 extends perpendicularly from the second portion 70 of the corner fitting 68 toward the centerline L-L of the housing 26. In some embodiments, the second terminal 74 may extend beyond the outer perimeter 13 of the varistor body 12. For example, where the varistor body 12 is based on 18mm (diameter) ceramic "13", the second terminal 74 may extend beyond the perimeter 13. However, it should be appreciated that in other embodiments, such as where a 20mm ceramic "13" is used, the second terminal 74 may not protrude so far.

Turning now to fig. 10, another embodiment of the first end 36 of the spring element 35 will be described in more detail. As shown, the first end 36 may include a set of

protrusions

75, 76 extending outwardly from the first terminal 45. In this embodiment, the

protrusions

75, 76 extend perpendicularly or substantially perpendicularly from a surface 77 of the first terminal 45. During connection of the spring element 35 to the thermode, a thermal link material 48, such as a low temperature solder, may be provided between the

protrusions

75, 76. Without the

protrusions

75 and 76, the thermal link material 48 is easily squeezed away from the first end 36 when the spring element 35 is in contact with the hot electrode 18. More specifically, the

protrusions

75, 76 maintain a specified gap between the terminal 45 and the thermode 18 and ensure that sufficient thermal link material 48 is present to provide suitable weld strength at the intersection therebetween.

Turning now to fig. 11-12, another TPV device 110 in accordance with embodiments of the present disclosure will be described in more detail. As shown, the TPV device 110 includes many of the features previously described with respect to the TPV device 10 of fig. 1-10, and therefore, for the sake of brevity, will not be described in detail. In this embodiment, TPV device 110 includes a piezoresistor body 112 that takes the shape of a square or rectangle defined by a perimeter 113. The varistor body 112 includes a first electrode (not shown) disposed along a first side 116 and a hot electrode 118 disposed along a second side 120. The first lead 121 is electrically connected to the first electrode, and the second lead 122 is electrically connected to the hot electrode 118. In some embodiments, thermode 118 is a metallized layer of ceramic, silver, copper, aluminum, or copper plus aluminum.

The TPV device 110 can also include a terminal assembly 124 coupled to the varistor body 112. In some embodiments, terminal assembly 124 includes a housing 126 having sidewalls 128 and a base 130, where sidewalls 128 extend substantially around the perimeter of housing 126. The sidewall 128 and the base 130 define a central cavity 132 in which a spring element 135 is contained. The spring element 135 includes a first end 136 disposed within the housing 126 and a second end 137 extending outside of the housing 126, wherein the second end 137 is connected to the third lead 123.

As shown, when a thermal link element (e.g., solder) coupling spring element 135 to thermode 118 is below the melting point, a first terminal 145 at first end 136 of spring element 135 may be connected with thermode 118 through opening 144 of base 130 to maintain spring element 135 in physical/electrical contact with thermode 118. If the thermal link element exceeds the melting point, such as during an overcurrent event, the spring element 135 will disengage and move away (as shown) from the exposed portion of the hot electrode 118, thereby causing the third lead 123 to be disconnected from the power source. Although not shown, the TPV device 110 can also include a housing cover coupled to the housing 126 and/or the varistor body 112.

As further shown, the second end 137 of the spring element 135 also includes a second terminal 174 for electrically/physically coupling the spring element 135 with the third lead 123. In some embodiments, the second terminal 174 may include sidewalls 180, 181 defining a channel 173 for receiving an end of the third lead 123 therein. The second terminal 174 may extend perpendicularly from the second portion 170 of the corner joint 168 of the spring member 135, away from the centerline L-L of the housing 126. In some embodiments, second terminal 174 is separated from hot electrode 118 by a gap, which may be filled with an epoxy coating material or other isolating material to provide sufficient dielectric strength between second terminal 174 and hot electrode 118.

Terminal assembly 124 can include one or more terminal clips 151 secured to housing 126 and piezoresistor body 112. In some embodiments, terminal clip(s) 151 are substantially U-shaped fasteners that are secured to housing 126. In the embodiment shown in fig. 12, the terminal clip 151 may extend completely across the housing 126, wrapping around the side wall 128. In some embodiments, the terminal clip 151 may be provided within a recess 182 formed in the bottom surface 153 of the base 130 of the housing 126, and the outer surface 154 of the terminal clip 151 may be secured (e.g., by high temperature solder) to the varistor body 112. In some embodiments, the terminal clip 151 is directly attached to the hot electrode 118. During assembly, the terminal clips 151 may be first secured to the varistor body 112 so that the housing 126 may then be snapped into place. In some embodiments, the terminal clip 151 may comprise pre-tinned SUS or pre-tinned steel.

Turning now to fig. 13-15, TPV device 210 in accordance with embodiments of the present disclosure will be described in more detail. As shown, the TPV device 210 includes a varistor body 212, in this embodiment, the varistor body 212 has a circular or disc shape defined by an outer periphery 213. The varistor body 212 includes a first electrode (not shown) disposed along a first side 216, and a hot electrode 218 disposed along a second side 220. The first lead 221 is electrically connected to the first electrode, and the second lead 222 is electrically connected to the hot electrode 218. In some embodiments, thermode 218 is a metallized layer of ceramic, silver, copper, aluminum, or copper plus aluminum.

The TPV device 210 can also include a terminal assembly 224 coupled to the varistor body 212. In some embodiments, the terminal assembly 224 includes a housing 226 having sidewalls 228 and a base 230, wherein the sidewalls 228 extend substantially around the perimeter of the housing 226. The side wall 228 and the base 230 define a central cavity 232 in which a spring element 235 is contained. The spring member 235 includes a first end 236 disposed within the housing 226 and a second end 237 extending outside of the housing 226, wherein the second end 237 is connected to the third lead 223. As will be described in more detail below, the first terminal at the first end 236 may be connected with the thermode 218 through an opening of the pedestal 230 to couple the spring element 235 to the thermode 218 when a thermal link element (e.g., solder) coupling the spring element 235 to the thermode 218 is below a melting point. If the thermal link element exceeds the melting point, such as in the case of an overcurrent condition, the spring element 235 will release and begin to move, thereby disconnecting the third lead 223 from the power source.

The TPV device 210 also includes a housing cover 239 coupled to the housing 226 and/or the piezoresistor body 212. In some embodiments, the housing cover 239 may generally follow the shape of the housing 226. For example, the housing cap 239 may take a generally circular shape with the flat side 279 extending parallel or substantially parallel to the second lead 222. The flat side 279 may provide an area for the second lead 222 to access/contact the hot electrode 218. As best shown in fig. 14, the housing cover 239 may include an opening or slot 243 through the side wall 241 from which the second end 237 of the spring element 235 may protrude. Although not shown, the housing cover 239 and the housing 226 may be covered by a conformal epoxy or other high-isolation material.

Turning now to fig. 15-17, the terminal assembly 224 of the TPV device 210 in accordance with an embodiment of the present disclosure will be described in greater detail. As shown, terminal assembly 224 can include an inner electrode 283 disposed between hot electrode 218 and housing 226. That is, the inner electrode 283 may include an outer surface 284 of the body 289 that is planar or substantially planar with the bottom surface 253 of the pedestal 230 of the housing 226. The body 289 can be directly coupled to the thermode 218, for example, using high temperature solder. In some embodiments, the housing 226 may include a recessed region 286 sized to receive the inner electrode 283 therein.

As shown, inner electrode 283 may include a front tab 295, a third terminal 285, and a terminal tab 287, wherein third terminal 285 and terminal tab 287 extend perpendicularly or substantially perpendicularly from body 289. The third terminal 285 is configured to extend through an opening 244 provided through the base 230 of the housing 226. During use, the spring element 235 may be secured to the third terminal 285 of the inner electrode 283, for example, using a thermal link material (not shown), such as a low temperature solder. When the thermal link material is below the melting point, physical/electrical contact between the third terminal 285 and the spring element 235 is maintained. However, when third terminal 285 heats up and exceeds the melting point of the thermal link material, the thermal link material melts and begins to flow, creating an insulating gap between third terminal 285 and spring element 235. That is, during an overcurrent event, the first end 236 of the spring element 235 begins to move away from the third terminal 285 due to the biasing spring force of the spring element 235.

The housing 226 of the terminal assembly 224 may include first and

second support walls

257, 258, the first and

second support walls

257, 258 defining a passage 259 for receiving and securing the spring element 235 therein. The channel 259 extends into an opening or slot 260 provided through the side wall 228 to allow the second end 237 of the spring member 235 to extend outside of the housing 226 for connection with the third lead 223. The housing 226 also includes a support post 262 adjacent to and extending from the first support wall 257. As shown, the spring element 235 is bent at least partially around the support post 262 to provide tension to the first end 236 of the spring element 235. In some embodiments, the housing 226 may be a high temperature plastic or resin, such as polyphenylene sulfide (PPS), Liquid Crystal Polymer (LCP), or the like.

As further shown, the housing 226 may include a support 290 extending from the inner surface 291 of the pedestal 230. The support 290 may be connected to the sidewall 228 and include three (3) sides partially surrounding the opening 244 and a third terminal 285. Support 290 acts as a physical support or barrier for third terminal 285 while still allowing access to third terminal 285 through spring element 235.

To accommodate the terminal tabs 287, the housing 226 can also include a cover wall 292 extending from the inner surface 291 of the base 230. Once the inner electrode 283 is coupled to the housing 226, the terminal tab 287 extends into an internal slot (not shown). Terminal tab 287 can be configured symmetrically with third terminal 285 and provide additional support to inner electrode 283 once coupled to housing 226. As shown, to securely attach the inner electrode 283 to the housing 226, each of the third terminal 285 and the terminal tab 287 may include a fastener, clasp, or surface feature 294 that extends outward to engage with a corresponding fastening feature (not shown) within the support 290 and the cover wall 292, respectively. Further, in some embodiments, the front tab 295 of the inner electrode 283 may extend into an alignment notch 296 formed in the body 289 of the housing 226.

Turning now to fig. 18, the spring element 235 according to embodiments of the present disclosure will be described in more detail. As shown, the spring element 235 may be a flat spring terminal that includes a central portion 265 extending between a first end 236 and a second end 237. The central portion 265 may include one or more bends or curves provided to mitigate stress concentrations and temperature fluctuations due to fatigue. For example, the central portion 265 may include a first bend 266 proximate the first end 236, and a second bend 267 disposed between the first bend 266 and the second end 237, wherein the second bend 267 may include a spring groove 297 to facilitate bending and reduce stress at that point along the spring element 235. Second bend 267 may be located proximate an angular joint 268, the angular joint 268 having a first portion 269 configured to extend through a channel 259 of housing 226 and a second portion 270 configured to extend through slot 260. As shown, the protrusion 250 may extend perpendicularly away from the first end 236 to enable contact with the third terminal 285. Although not shown, the first end 236 and the protrusion 250 may include a covering of thermal link solder.

In some embodiments, the corner joint 268 has a first height dimension H1, the first height dimension H1 being larger/longer than a second height dimension H2 adjacent the central portion 265 and the first end 236. The height difference between H1 and H2 is designed to allow the spring element 235 to swing freely with minimal friction between the central portion 265 and the base 230 of the housing 226 during an overcurrent event.

As further shown, the second end 237 of the spring element 235 may include a second terminal 274 for electrically/physically coupling the spring element 235 with a third lead (not shown). In some embodiments, the second terminal 274 may include

sidewalls

280, 281 defining a channel 273 for receiving a third lead therein. The second terminal 274 extends generally perpendicularly from the second portion 270 of the corner joint 268, such as toward the centerline of the housing 226. In some embodiments, for example, as shown in fig. 15, the second terminal 274 may extend beyond the outer perimeter 213 of the varistor body 212.

Turning now to fig. 19-21, another TPV device 310 in accordance with embodiments of the present disclosure will be described in more detail. As shown, the TPV device 310 includes a varistor body 312, in this embodiment, the varistor body 312 has a square or rectangular shape defined by an outer perimeter 313. The varistor body 312 includes a first electrode (not shown) disposed along a first side 316, and a hot electrode 318 disposed along a second side 320. The first lead 321 is electrically connected to the first electrode, and the second lead 322 is electrically connected to the hot electrode 318. In some embodiments, hot electrode 318 is a metallized layer of ceramic, silver, copper, aluminum, or copper plus aluminum.

The TPV device 310 can also include a terminal assembly 324 coupled to the varistor body 312. In some embodiments, the terminal assembly 324 includes a housing 326 having sidewalls 328 and a base 330, wherein the sidewalls 328 extend substantially around the perimeter of the housing 326. The sidewall 328 and base 330 define a central cavity 332 in which a spring element 335 is contained.

As shown, terminal assembly 324 can include an inner electrode 383 disposed between hot electrode 318 and housing 326. That is, inner electrode 383 may include an outer surface that is coupled to body 389 of hot electrode 318 and that extends planar or substantially planar along a bottom surface of base 330 of housing 326. The inner electrode 383 may include a front tab 395, and a third terminal 385 and a terminal tab 387 extending perpendicularly or substantially perpendicularly from the main body 389. In some embodiments, the housing 326 may include a recessed area in the base 330 sized to receive the inner electrode 383 therein.

TPV device 310 also includes a housing cover 339 coupled to housing 326 and/or piezoresistor body 312. As shown, the side walls 328 of the housing 326 may engage the housing cover 339 using a set of fasteners 398. In some embodiments, the set of fasteners 398 includes one or more tabs or protrusions that snap into corresponding openings. The housing cover 339 may also include one or more relief slots 399 to provide flexibility to the housing cover 339 when the housing cover 339 is attached to the housing 326.

As shown, the housing cover 339 may generally follow the shape of the housing 326, although embodiments herein are not limited to any particular shape. For example, the housing cover 339 may take a generally square or rectangular shape. As best shown in fig. 19, the housing cover 339 may include one or more flat sides 379 that extend parallel or substantially parallel to the ends of the second leads 322. The flat side 379 can provide an area for the second lead 322 to access/contact the hot electrode 318. The housing cover 339 may include an opening or slot 343 through the flat side 379 from which the spring element 335 may protrude. Although not shown, the housing cover 339 and the housing 326 may be covered by a conformal epoxy or other high isolation material.

Turning now to fig. 21, terminal assembly 324 of TPV device 310 in accordance with embodiments of the present disclosure will be described in greater detail. The spring element 335 includes a first end 336 disposed within the housing 326 and a second end 337 extending outside of the housing 326, wherein the second end 337 is connected to the third lead 323 (fig. 19-20). As shown, the third terminal 385 may extend through an opening 344 provided through the base 330 of the housing 326. The spring element 335 is configured to be secured to the third terminal 385 of the inner electrode 383, for example using a thermal link material (not shown), such as low temperature solder. When the thermal link material is below the melting point, physical/electrical contact between the third terminal 385 and the spring element 335 is maintained. However, when the third terminal 385 heats up and exceeds the melting point of the thermal link material, the thermal link material melts and begins to flow, creating an insulating gap between the third terminal 385 and the spring element 335. That is, during an overcurrent event, the first end 336 of the spring element 335 begins to move away from the third terminal 385 due to the biasing spring force of the spring element 335.

The housing 326 of the terminal assembly 324 may include first and

second support walls

357, 358, the first and

second support walls

357, 358 defining a channel 359 for receiving and securing the spring element 335 within the housing 326. The passage 359 extends into an opening or slot 360 provided through the sidewall 328 to allow the second end 337 of the spring element 335 to extend outside of the housing 326 for connection with the third lead 323. The housing 326 also includes support posts 362 adjacent to and extending from the first support wall 357. As shown, the spring element 335 is bent at least partially around the support post 362 to provide tension to the first end 336 of the spring element 335.

As further shown, the housing 326 may include a support 390 extending from an inner surface 391 of the base 330. The support 390 may be connected to the sidewall 328 and include three (3) sides partially surrounding the opening 344 and a third terminal 385. The support 390 acts as a physical support or barrier for the third terminal 385 while still allowing access to the third terminal 385 through the first end 336 of the spring element 335.

To receive the terminal tabs 387, the housing 326 can also include a cover wall 392 extending from the inner surface 391 of the base 330. Once the inner electrode 383 is coupled to the housing 326, the terminal tab 387 extends into an interior slot (not shown) of the cover wall 392. In this embodiment, the terminal tab 387 is disposed structurally symmetrical to the third terminal 385 and provides additional support to the inner electrode 383 once coupled to the housing 326. To securely attach the inner electrode to the housing 326, each of the third terminal 385 and the terminal tab 387 may include a fastener, clasp, or surface feature (not shown) that extends outward to engage with a corresponding fastening feature within the support 390 and the cover wall 392, respectively. Further, in some embodiments, the front tab 395 of the inner electrode 383 may extend into an alignment notch 396 formed in the main body 389 of the housing 326.

Turning now to fig. 22, the spring element 335 according to an embodiment of the present disclosure will be described in more detail. As shown, the spring element 335 may be a flat spring terminal that includes a central portion 365 extending between the first end 336 and the second end 337. The central portion 365 may include one or more bends or curves provided to mitigate stress concentrations and temperature fluctuations due to fatigue. For example, the central portion 365 may include a first bend 366 proximate the first end 336, and a second bend 367 disposed between the first bend 366 and the second end 337, wherein the second bend 367 may include a spring slot 397 to facilitate bending and reduce stress at that point along the spring member 335. Second bend 367 may be located adjacent channel portion 368, channel portion 368 being substantially straight and configured as a channel 359 extending through housing 326. Channel portion 368 may include side tabs 369, side tabs 369 configured to engage side wall slots 361 (fig. 21) to secure spring element 335 within housing 326. As shown, the side tabs 369 may extend perpendicularly or substantially perpendicularly from the tunnel portion 368. As further shown, the first end 336 may include a protrusion 350 extending away from the spring element 335 to enable contact with the third terminal 385. Although not shown, first end 336 and protrusion 350 may include a layer of cover or solder material.

In some embodiments, the channel portion 368 has a first height dimension H1, the first height dimension H1 being larger/longer than a second height dimension H2 adjacent the central portion 365 and the first end 336. The height difference between H1 and H2 is designed to allow the spring element 335 to swing freely with minimal friction between the central portion 365 and the base 330 of the housing 326 during an overcurrent event.

As further shown, the second end 337 of the spring element 335 may include a second terminal 374 for electrically/physically coupling the spring element 335 with a third lead (not shown). In some embodiments, second terminal 374 may include

sidewalls

380 and 381 that define a channel 373 for receiving a third lead therein. The second terminals 374 extend generally parallel from the channel portion 368. In some embodiments, the second terminal 374 is supported above the hot electrode 318 or remote from the hot electrode 318. For example, the second terminal 374 may be separated from the hot electrode 318 by a gap, which may be filled with an epoxy coating material or other isolating material to provide sufficient dielectric strength between the second terminal 374 and the hot electrode 318.

In summary, the TPV device of the present disclosure provides a flat spring terminal that can be quickly disconnected from a ceramic hot electrode in response to an overcurrent event to provide an open circuit to a power source. Embodiments of the present disclosure provide at least the following advantages. First, TPV equipment is relatively simple to assemble and allows for automated production, thereby reducing manufacturing costs. Second, the TPV device has high reliability under abnormal overvoltage conditions due to the configuration of the spring element. Third, the TPV device provides a fast response to overheating since the spring element is soldered directly to the ceramic thermal metallization layer. Fourth, TPV devices provide drop-in replacements for existing TMOV due to the same pin configuration and profile, and due to the use of thermal clips. Fifth, the TPV device provides a robust disconnect due to the long open circuit distance once the spring element is free to oscillate within the housing. Sixth, one component module can cover all rated voltages for one disk size.

Although the present disclosure has been described with reference to certain aspects, numerous modifications, alterations, and changes to the described aspects may be made without departing from the scope and spirit of the present disclosure as defined in the appended claims. Accordingly, it is intended that the disclosure not be limited to the described versions, but that it have the full scope defined by the language of the following claims, and equivalents thereof. Although the present disclosure has been described with reference to certain aspects, numerous modifications, alterations, and changes to the described aspects may be made without departing from the spirit and scope of the present disclosure as defined in the appended claims. Accordingly, it is intended that the disclosure not be limited to the described aspects, but that it have the full scope defined by the language of the following claims, and equivalents thereof.

Claims

1. A thermally protected varistor apparatus, comprising:

a varistor body comprising:

an electrode disposed along the first side; and

a hot electrode disposed along a second side opposite the first side, wherein a first lead is electrically connected to the electrode and a second lead is electrically connected to the hot electrode; and

a terminal assembly coupled to the piezoresistor body, the terminal assembly comprising:

a housing comprising a sidewall and a base, wherein an opening is provided in the base;

an inner electrode disposed between the hot electrode and the case; and

a spring element having a first end disposed within the housing and a second end extending outside of the housing, wherein a first terminal at the first end is connectable with the thermode through the opening of the base to maintain the spring element in physical contact with the thermode when a thermal link material coupling the spring element with the thermode is below a melting point,

wherein a second terminal at the second end is connected to a third lead,

wherein the inner electrode includes:

a body extending along the base of the housing; and

a third terminal and a terminal tab extending substantially perpendicularly from the main body, wherein the third terminal is in physical contact with the spring element when the thermal link material is below the melting point.

2. The thermally protected pressure sensitive resistor apparatus of claim 1, the terminal assembly further comprising a housing cover coupled to the housing.

3. The thermally protected piezoresistor device of claim 1, wherein the thermal link material melts and flows above the melting point to create an insulating gap between the thermode and the first terminal of the spring element.

4. The thermally protected pressure sensitive resistor apparatus of claim 1, the housing of the terminal assembly further comprising:

a set of support walls defining a channel for receiving the spring element;

a slot extending through the sidewall, the slot receiving the spring element from the channel; and

a support post adjacent to the set of support walls, wherein the spring element is at least partially curved around the support post.

5. The thermally protected varistor apparatus of claim 1, wherein the thermal link material is a low temperature solder.

6. The thermally protected varistor apparatus of claim 1, the terminal assembly further comprising a terminal clip coupling the varistor body with the housing.

7. The thermally protected varistor apparatus of claim 2, wherein the housing cover comprises at least one flat side extending substantially parallel to the second lead.

8. The thermally protected pressure sensitive resistor apparatus of claim 1, the housing of the terminal assembly further comprising:

a support extending from an inner surface of the base, the support extending around the opening in the base and the third terminal of the inner electrode; and

a cover wall extending from the inner surface of the base, the cover wall receiving the terminal tab of the inner electrode.

9. The thermally protected piezoresistor device of claim 1, wherein the base of the housing of the terminal assembly comprises a guide region recessed into the base, and wherein the guide region receives the first end of the spring element when the spring element is disconnected from the hot electrode.

10. The thermally protected pressure sensitive resistor apparatus of claim 2 wherein the side walls of the housing engage the housing cover using a set of fasteners.

11. The thermally protected piezoresistor device of claim 1, wherein the first end of the spring element comprises an outwardly extending protrusion, and wherein the thermal link material is provided adjacent to the protrusion on the spring element.

12. A thermally protected varistor apparatus, comprising:

a varistor body comprising:

an electrode disposed along the first side; and

a housing comprising a side wall and a base, wherein an opening is provided in the base for electrical connection with the hot electrode;

an inner electrode disposed between the hot electrode and the case; and

a spring element having a first end disposed within the housing and a second end extending outside of the housing through a slot in the sidewall, the first end being connectable with the hot electrode through the opening of the base to maintain physical contact of the spring element with the hot electrode via a thermal link material when the thermal link material is below a thermal threshold,

wherein a second terminal at the second end is connected to a third lead,

wherein the inner electrode includes:

a main body; and

a third terminal and a terminal tab extending substantially perpendicularly from the main body, wherein the third terminal is in physical contact with the spring element when the thermal link material is below the thermal threshold.

13. The thermally protected varistor apparatus of claim 12, the terminal assembly further comprising a housing cover coupled to at least one of the housing and the varistor body.

14. The thermally protected piezoresistor device of claim 12, wherein the thermal link material melts and flows above the thermal threshold to create an insulating gap between the thermode and the first end of the spring element.

15. The thermally protected pressure sensitive resistor apparatus of claim 12, said housing of said terminal assembly further comprising:

a set of support walls defining a channel for receiving the spring element; and

16. The thermally protected piezoresistor device of claim 12, wherein the thermal link material is a low temperature solder disposed on a surface of the first end of the spring element.

17. The thermally protected varistor apparatus of claim 12, said terminal assembly further comprising a terminal clip coupling said varistor body with said housing.

18. The thermally protected pressure sensitive resistor apparatus of claim 12, said housing of said terminal assembly further comprising:

19. The thermally protected piezoresistor device of claim 12, wherein the first end of the spring element comprises an outwardly extending protrusion, and wherein the thermal link material is provided adjacent to the protrusion.